While previous studies have suggested that vitamin D may play a role in controlling normal breast cell growth and may even be able to stop breast cancer cells from growing, new research by a team from Roswell Park Cancer Institute (RPCI) and four other institutions, shows that vitamin D supplementation may benefit black women the most.
For the study, which was published in the journal Breast Cancer Research, scientists compared levels of vitamin D in the blood of women without breast cancer and found that severe vitamin D deficiency in African-American women was almost six times more common than in European-American women. Because low levels of vitamin D can also be caused by disease or by treatment, however, the researchers decided to focus their studies on genetic variations in the vitamin D receptor (VDR) and the enzymes responsible for breaking down vitamin D in the body.
What they found: African-American women with the highest levels of vitamin D also had a specific variation in VDR that cut their breast cancer risk in half, compared to women without it.
"Our results show that these genetic variations, which contribute to the function of vitamin D, are strongly associated with ER-negative breast cancer and may contribute to the more aggressive breast cancer features seen in African-American women," said Song Yao, PhD, Research Assistant Professor of Oncology and one of the authors of the study.
Estrogen receptor-negative (ER-negative) tumors are referred to as "hormone insensitive" or "hormone resistant," meaning that they generally do not respond to hormone treatments such as tamoxifen or aromatase inhibitors. African-American women have a disproportionately higher risk of developing these aggressive and difficult-to-treat breast cancers, for reasons that continue to be explored.
According to a new report by the Centers for Disease Control and Prevention (CDC), close to a third of African-Americans are deficient in vitamin D. With almost 90 percent of Vitamin D being made through sun exposure, African Americans are at greater risk for this deficiency since pigmentation in the skin inhibits skin cells' ability to produce the nutrient in this way.
For most adults, 600 IU of vitamin D is recommended daily and can be found in supplements (and fortified foods), in two different forms: D2 (ergocalciferol) and D3 (cholecalciferol).